MAX1874(2003) データシートの表示（PDF） - Maxim Integrated

部品番号

コンポーネント説明

メーカー

MAX1874
(Rev.:2003)

Dual-Input, USB/AC Adapter, 1-Cell Li+ Charger with OVP and Thermal Regulation

Maxim Integrated 

Dual-Input, USB/AC Adapter, 1-Cell

Li+ Charger with OVP and Thermal Regulation

acceptable range. To verify that the input voltage is

stable, DCOK has an internal delay of 20ms before con-

necting power to DCLV. DCOK remains operational

when EN is low (charger off).

USB Power-OK (UOK)

UOK is an active-low, open-drain output that goes low

to indicate that VUSB is valid (greater than 4V). UOK

remains operational when EN is low (charger off). An

external 10kΩ pullup resistor keeps UOK high until it is

certain that power is within the acceptable range. UOK

can be used as a logic output, or to control a MOSFET

that switches USB power directly to the system load

when the MAX1874 is powered from a USB source (Q1

in Figure 4).

Bypass (BYP)

BYP is the bypass connection for the MAX1874’s inter-

nal power rail. Bypass to GND with a 2.2µF or greater

capacitor. The voltage at BYP is supplied from either

DCLV or USB through an internal 5Ω switch network.

Power On (PON)

PON goes high when VDC or VUSB is within its normal

operating range. PON can be used as a logic output to

indicate power is connected or can drive an external

P-channel MOSFET that switches the system load from

the battery to an external source when power is applied.

See Q3 in Figures 4 and 5.

Charging Current

Precharge Current

When the MAX1874 is powered with a battery connect-

ed, the IC first detects if the cell voltage is ready for full

charge current. If the cell voltage is less than the pre-

qual level (3V typ), the battery is precharged with a

50mA current until the cell reaches the proper level.

The full charging current, as set by USEL or DCI, is

then applied.

USEL

The charging current from the USB source is selected

by USEL. A USB source can supply a maximum of

100mA or 500mA. USB hosts and powered hubs typi-

cally supply 500mA, while unpowered hubs supply

100mA. A logic low on USEL selects a 100mA maximum

charging current. A logic high on USEL selects a 500mA

maximum charging current.

DCI

When charging from the DCLV input, the voltage at DCI

sets the charge current. The voltage-to-current transfer

ratio from DCI to BATT is 1A/VREF. The DCI pin should

be connected to a resistive divider from REF to DCI to

GND (R5 and R6 in Figures 2 and 4). In this configura-

tion, IBATT is as follows:

IBATT = [R6 / (R5 + R6)] Amps

R5 and R6 should total 25kΩ or more to minimize loading

on REF. Connecting DCI directly to REF results in a 1A

charge current.

Battery Full (CHG)

CHG is low when the MAX1874 is charging in either the

prequal or full-charging state. CHG then goes high

when the charging current falls below a percentage of

the set fast-charge current (Table 2) and the charger is

in voltage mode (VBATT near 4.2V). The CHG current

threshold is a function of the charger mode. When

charging from a DC source, CHG goes high when

IBATT falls to 12.5% of the current set by VDCI and the

charger is in voltage mode (VBATT near 4.2V). When

charging from a USB source with USEL high, CHG

goes high when IBATT falls to 125mA and the charger is

in voltage mode. If the MAX1874 is charging from a

USB source with USEL low, CHG goes high when the

charger enters voltage mode.

Package Thermal Limiting

On-chip thermal limiting in the MAX1874 simplifies PC

board layout and allows charging rates to be automati-

cally optimized without constraints imposed by worst-

case minimum battery voltage, maximum input voltage,

and maximum ambient temperature. When the

MAX1874 thermal limit is reached, the charger does not

shut down but simply reduces charging current. This

allows the board design to be optimized for compact

size and typical thermal conditions. The MAX1874

reduces charging current to keep its die temperature

below +105°C.

Table 2. CHG Battery Full Indication

CHARGING SOURCE

CHARGE CURRENT THRESHOLD FOR CHG GOING HIGH

DCLV Charging

12.5% of Charge Current Set by DCI and Charger in Voltage Mode

USB Charging 500mA (USEL high) 125mA and Charger in Voltage Mode

USB Charging 100mA (USEL low) Charger in Voltage Mode

Note: CHG does not go high when charge current is reduced by the thermal regulation loop.

______________________________________________________________________________________ 11

Share Link: